Los primeros estadios de vida de la merluza Merluccius hubbsi Marini, 1933 en el Mar Argentino como aporte al conocimiento de su reclutamiento y estructura poblacional.
The early life history of hake Merluccius hubbsi Marini, 1933 in the Argentine Sea for understanding its recruitment and population structure.Hake is the most important demersal species in the Argentine Sea. Its catch in1996 exceeded 600.000 t and it seemed overfished.The study of the hake early life history was developed in two aspects,reproductive analysis like fecundity and spawning frequency, and early stages(eggs, early larvae, late larvae and juveniles) distribution and abundance.Hake is an indeterminate batch spawner, wich spawns all over the year, with two peak spawning times, one during winter (May-July) in the northern area of its wide distribution (35°-38°S) and the other in summer (October-March) in the north Patagonia coastal waters (43°-45°S). Female relative fecundity between 35-38 cm of total length, expressed as ovocites per ovary free-weight, varied between 520 to 640 and its batch fecundity ranged from 267400 to 432240 ovocites per spawn. The spawning frequency was estimated in 22 days. Considering the presence of post ovullatory follicles in the samples and stage I eggs in the plankton, hake spawns all over the day with a matinal peak. Male dominated schools after spawning have finished. The hatching time in reared eggs varied between 5,01 days at 10°C to 3,1 days at18°C. The analysis of 1470 ichthyoplankton samples obtained in 39 research cruises between 1973 to 1989 allowed to study monthly the main important hake spawning and nursery areas. The eggs were caught in the northern area (34°-41°30'S)during April (39°-37°S), May - June (37°-35°S) and July -August (34°-35°S). Hake spawns in shelf, between 50 to 160 m depth, where temperatures at 10 m ranged from 9,4 to 13,3°C. During May, September and November it spawns between 40°-42°S. In the San Matías Gulf northern area hake eggs were caught in September and October. In the southern platform between 41°30' to 47°S it was detected an important spawning area off southwestern Peninsula Valdes and coastal Chubut and another less important in the southern San Jorge Gulf, both during November to March, with peaks in December. In summer hake spawns between 40 to 60 m depth, and temperatures at 10 m ranged from 13 to 18°C. The late larvae and early juveniles distribution is consistent with spawning areas.The different spawning areas are related to very particular oceanographic conditions, wich determine an appropiate reproductive habitat associated with retention areas and disponibility of food. The winter spawning area is influenced by different fronts (shelf break and termohaline)and the Ekman's transport to the coast prevents larval drift to subtropical waters. The summer spawning area is influenced in the south and southwestern Península Valdés by tidal fronts, while in San Matías and San Jorge Gulfs by termohaline ones.The spawning times and areas are related with different hidrographic processes, wich are associated with different adult groups or stocks, supporting the hypothesis that hake presents multiple stocks in the Argentine Sea. In the most important summer spawning area, related with tidal fronts, the eggs and larvae are distributed in frontal and stratified areas where differences of surface and bottom temperatures ranged between 3,8 to 4°C.Eggs in different stages and early larvae were distibuted in the whole water column.The presence of larvae and juveniles in different seasons and areas in the Argentine Sea allowed to associate to the hake recruitment process the match-mismatch production cycles (Cushing, 1972) and member vagrant hypothesis (Sinclair Iles, 1989).Because of the adults reproductive behavior and the early life history stages distribution, the hake may be considered as a succesful spawner, wich supports an important fishery pressure.